A typical electrochromic device comprises at least five superimposed layers deposited on one substrate or positioned between two substrates in a joined together configuration. The central part of the five-layer electrochromic stack an ion conductor (e.g. an electrolyte). The ion conductor is in contact with an electrochromic film, capable of conducting electrons as well as ions. On the other side of the ion conductor is an electron and ion conducting counter electrode film serving as an ion storage layer. The central three-layer structure is positioned between electron conducting layers. Such a device is colored/bleached by applying an external voltage pulse between the electron conducting layers on the two sides of the stack, causing the electrons and ions to move between the electrochromic layer and the counter electrode layer. Applications of electrochromic devices include architectural windows, information displays, light filters and modulators, rear-view mirrors, sunroofs and windows in vehicles, eyewear, helmet visors, ski goggles, surfaces with variable thermal emissivity or camouflage.
Historically, the first electrochromic coatings were deposited on glass substrates. The possibility of using plastic substrates is described, for example, in WO9923528. Electrochromic devices on plastic substrates are characterized by their light weight, flexibility, and the ease of cutting to complex shapes.
As mentioned above, the electrochromic device is operated by applying a voltage between the two electron conducting layers. In order to do this, the electron conducting layers have to be electrically contacted in some way. A typical thickness of the electron conducting layers is in the range of 50-400 nm, which means that the layers themselves do not have the mechanical strength of supporting any mechanical forces. Another aspect is the lateral distribution of the applied of voltage, influencing the homogeneity of the device operation. Improved homogeneity is typically achieved by adding e.g. a bus bar to the electrochromic stack in electrical connection with the electron conducting layer.
A typical procedure in prior art for contacting the electron conducting layers in a thin electrochromic device is to provide an electrically conducting means in contact with the electron conducting layers and/or a portion of a bus bar. The electron conducting layers are typically allowed to protrude outside the actual side of the operational electrochromic device, i.e. through the edge seal of the stack of layers of the electrochromic device, and the connection to the connection means is performed outside the stack. Another approach is to let parts of the connection means extend into the actual electrochromic stack, primarily for thick devices. Typical examples can be found in the published US patent application 2004/0218247. For thicker substrates, the bus bars can also continue around the side edge of the device, whereby contacting can be performed at the side edges.